Vehicles of the type involved herein are classified in class 214, subclass 82 et seq. For relevant prior art, see U.S. Pat. Nos. 3,796,330, 4,004,703 and 4,199,297. The vehicles disclosed in said patents suffer from one or more of the following disadvantages.
To ensure a vertical disposition and provide parallel guidance of the pushing means in said patents, synchronized chains or ropes are employed, which results in an arrangement which is very expensive and difficult to maintain. In U. S. Pat. No. 3,796,330, the arrangement creates a considerable reduction of cargo space which results in a loss of payload. Due to a moment arm effect wherein the prior pushing means tends to rotate about vertical axes, lateral connecting beams are provided to resist such rotation. One of said connecting beams is adjacent the floor and lift trucks must pass over the same when loading the vehicle.
The prior art vehicles due to their construction have control problems due to side wall bulge. It is difficult to have access to cables, chains and the like for maintenance purposes. The side walls of the vehicles have projections which rub against the compressible product thereby damaging the same.
The structural strength of the conventional, standard dry cargo semi-trailers is not sufficient to withstand the loads imposed upon them by these loading systems. Consequently, specially engineered and constructed trailers must be used, resulting in a much higher cost. In other words, these loading systems cannot be economically added to standard construction semi-trailers.
The system described in U.S. Pat. No. 4,004,703 has one major drawback. The "pushing means" (or, in this case, it would actually be "pulling means") has no mechanical, built-in provision for returning to the open (rear) end of the trailer enclosure to receive the next load and to perform another loading (compression) cycle. The "pull cables" must be returned to the rear by hand (impossible due to the resisting forces involved) or by some mechanical device such as a forklift truck dragging them out. The basic problem, of course, is that the actuating mechanism, block and tackle, is a "one way motion" device. It can pull ropes or cables, but it cannot push them back.
The system described in U.S. Pat. No. 4,199,297 overcomes the drawbacks of the prior art. It provides for two trolleys disposed on each wall of the trailer arranged for reciprocal motion in a longitudinal direction along each wall to compress the load and return to the open end of the trailer after a bulkhead is secured to retain the load in its compressed state. However, after continued use the chains providing the motive force to the trolleys tend to wear and/or stretch resulting in the loss of their original tension. Also, a single drive motor tends to overload in certain circumstances. These problems and the fact that the operator cannot directly watch the compression process coexist as deficiencies which the new system of the present invention overcomes.